[Users] Error Handling with Parallel Forking

[Chris Heiser]

Hello gurus,

I'm attempting to do some rather crazy parallel forking and have found a 
few issues I'm hoping to solve.  I thought I'd solicit some advice from 
the experts.

Some background:

Each device registers with its own unique information.  No two devices 
share the same credentials.  Since a random user might want their number 
sent to multiple phones, and maybe even a cell phone, I've done the 
following:

         if(method=="INVITE" && !isflagset(5))
         {
                 if(avp_db_load("$ru/username","fork"))
                 {
                         t_on_branch("1");
                         avp_pushto("$ru/username","$avp(s:fork)/g");
                 };
         };

Then the branch route looks like:

branch_route[1]
{
         setflag(5);
         route(3);
}

The idea here is the fork avp contains one or more possible destinations, 
but we don't store a complete URI here.  The branch route sends us back 
through the normal routing logic to lookup local users on the system, and 
maybe route something to an external PSTN gateway, or another proxy.

The problem:

I haven't found a way to gracefully handle the event when one of the 
possible destinations is a device that hasn't registered.  Say we allow 
the user to have a soft client, so we add the username to the list of fork 
avps.  If the device isn't registered, I have 2 options:

1)  Use a default route
2)  Detect that I should know who this is, and error out

Either way, an error is produced, but I don't see a good way of detecting 
if we should push the 404, or generate a 404 back to the client.  The 
polite method would be:

Are there other branches still going?
   If yes, just exit this branch
   If no, relay, or generate an error back to the client

So my question is how to do this last part.  Am I crazy for even thinking 
about doing this in OpenSER?  BTW, I'm using v1.1.1

--Chris